Liver ischemia/reperfusion injury (IRI) occurs in multiple clinical settings and contributes to patient morbidity/mortality by causing primary liver failure and graft rejection. However, despite extensive research of the disease pathogenesis over the years, no effective therapies are currently available to ameliorate liver IRI in the clinics. Liver IRI is dependent on the activation of local pro-inflammatory immune response mediated by liver macrophages; Kupffer cells (KCs) and the innate immune receptor TLR4. Although exogenous Ags are not required for the pathogenesis of liver IRI, adaptive immune component CD4 T cells are indispensible, which require CD154, but not IFN-g, for their function. Thus, the question arises as to how CD4 T cells are activated and function in this liver innate immune response. We have recently shown that liver IRI is critically dependent on the activation of the CXCL10/CXCR3 signaling pathway, which is triggered in liver by IR via the TLR4- IRF3-type I IFN pathway. The disruption of CXCL10/CXCR3 signaling results in two distinctive phenotypes in the pathogenesis of liver IRI: liver pro-inflammatory immune response is selectively suppressed in CXCL10 KO mice; while post-ischemic neutralization of CXCL10 in WT mice protects livers from IRI without diminishing liver proinflammatory immune response. CXCL10/CXCR3 signaling is well known for its chemotactic function in Ag-specific immune responses by recruiting activated T cells into the inflammation site. We propose that it may also serve as the link between KCs and CD4 T cells in liver TLR4 response against IR by triggering liver CD4 T cells to express CD154 and activate CD40 in KCs and hepatocytes, which facilitates the early pro-inflammatory immune activation and the secondary inflammation induced hepatocellular injury. By employing well-defined murine liver IRI model in vivo and macrophage/T cell/hepatocyte cultures/co-cultures in vitro, we will analyze these distinctive regulatory mechanisms of CXCL10/CXCR3 signaling in liver IRI at both cellular and molecular levels in two specific aims. (1). CXCL10/CXCR3 signaling facilitates liver pro-inflammatory immune activation by identifying its target cells in the liver and its regulated immune functions in target cells; (2). CXCL10/CXCR3 signaling facilitates inflammation-induced hepatocellular injury by identifying its regulated cytoprotective pathways/genes in hepatocytes. Both the direct effects of CXCL10/CXCR3 signaling in KCs, T cells and hepatocytes as well as the indirect effect via CD4 T cell interactions with KCs and hepatocytes will be determined. Results may provide us answers to one of the key questions in the disease mechanism of liver IRI, i.e., how CD4 T cells are activated and function in liver TLR4-mediated innate immune response, as well as novel therapeutic targets for clinical application to ameliorate liver IRI in patients. PUBLIC HEALTH RELEVANCE: Ischemia and reperfusion injury (IRI) in the liver is a common cause of liver failure, and occurs in many surgical procedures, including tumor resection, repair of trauma, and liver transplantation. Currently, there is no effective therapeutics to prevent or treat liver IRI in patients, due to the lack of complete understanding of the disease mechanism. This study dissects the immunological mechanism of liver IRI. Results will provide rationales for novel therapies to ameliorate liver IRI in clinics.